Mini-Mini Components

It once took half a dozen or more vacuum tubes, crammed into a bulky cabinet, to make an ordinary household radio. Today, postage-stamp-size electronic "chips," or integrated circuits, contain all the parts needed for far more complex electronic devices ranging from pocket calculators to missile guidance systems. But even these miracles of miniaturization may look gargantuan alongside the circuitry of the future. Scientists are now talking about turning individual molecules into electronic components.

To achieve this feat, Chemists Arieh Aviram of IBM's Thomas J. Watson Research Center and Mark A. Ratner of New York University propose making use of a well-known characteristic of the molecule: the higher the "binding energy" that holds it together, the less likely it is to lose electrons. The chemists recently told the American Physical Society that two or more small molecules with a large enough difference in binding energies might be combined into one large molecule that could perform electronic functions.

For a start, they are trying to make a rectifier, a simple device for changing the periodically reversing flow of electrons in alternating current (AC) into the one-way flow of direct current (DC). Like the cathode in ordinary vacuum tubes, one end of the molecular rectifier would act as a donor of electrons because it would be made out of a molecule that had a lower binding energy. The other end, carrying a higher binding energy, would serve as an anode, or electron acceptor. Thus, if an external alternating voltage were applied, the large molecule would act as a rectifier. It would allow electrons to flow in only one direction, from donor end to acceptor.

Achieving the precise spacing between donor and acceptor points to avoid the molecular version of a short circuit may be difficult, Aviram and Ratner admit. But, adds IBM Physicist Philip Seiden, chemists are already skilled at manipulating molecular structure and might be able to build molecular devices that will some day perform all the chores of today's tiny chips.

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